1. Field of the Invention
This invention relates to a wireless terminal, a base station, a wireless communication system, and a wireless communication method, and particularly relates to a method for saving power of the wireless terminal.
2. Related Art
A wireless LAN (Local Area Network) terminal has a power save mode (PS mode) for restraining power consumption. In a normal mode, the terminal can perform wireless communication all the time since the power is always turned on to transmit and receive data through the wireless LAN communication. In the PS mode, the terminal turns off the power for the communication when the data to be transmitted is not existent, but periodically turns on the power and receives a beacon from an access point at the intervals of one or a plurality of beacons in order to detect the existence or nonexistence of the data addressed to the terminal. The beacon includes information showing whether the access point has data addressed to the terminal. The terminal detects the information to receive the data. In this way, since small power is required except when receiving the beacon in the PS mode, power consumption in the PS mode is more restrained than in the normal mode (see Japanese Patent No. 4081679).
However, even when the above PS mode is used, the terminal consumes power by periodically turning on the power to receive the beacon regardless of whether or not the access point has the data addressed to the terminal. Accordingly, even when the data to be received is not existent for a long time, the terminal exhausts power if the terminal is not supplied with power.
Japanese Patent No. 4081679 suggests a method in which a power supply signal is used to supply power to the access point and the mobile terminal in a noncontact way so that the power consumed except when performing data communication is reduced. However, since the power supply signal is transmitted within a short distance of several meters, it is difficult to use the method in a telephone service using wireless LAN communication, for example.